Our study shows the influence of microplastics on global climate is currently very small, and a cooling effect dominates. The magnitude of microplastics' influence on climate varies in our climate model simulations, depending on assumptions we made about how the plastic fragments are distributed throughout Earth's atmosphere.īecause airborne microplastics research is so new, we had a limited number of studies to inform our research.
This presents additional questions whether microplastics could alter atmospheric chemistry by providing surfaces for chemical reactions to occur on, and how they interact with clouds. We don't know yet how far up into the atmosphere microplastics have reached, but an aircraft-based study found them at altitudes of up to 3.5km. The highest reported concentrations of airborne microplastics (thousands of fragments per cubic metre of air) were measured at urban sampling sites in London and Beijing. However, they can also absorb radiation emitted by the Earth, which means they contribute, in a very small way, to the greenhouse effect. We found that, overall, airborne microplastics are efficient at scattering sunlight, which implies a cooling effect on climate. One exception is soot (or black carbon), which is good at absorbing sunlight and has a warming effect.
Most types of aerosols in Earth's atmosphere scatter light - therefore in general, aerosols have partially offset greenhouse gas warming in recent decades. This has a cooling effect on Earth's climate. Initially, we expected airborne microplastics would scatter sunlight like most aerosols, which act like tiny disco balls and reflect sunlight back to space. This has led us to think of a plastic cycle: microplastics don't stay in soils, rivers, the ocean or air, but move between different parts of the Earth system. Researchers look for microplastics on a beach at Southend-on-sea near London in June 2019.
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